I was looking for a -Impact Riven on Riven market and I realized there were none available. Tried Semlar and the same happened there. Apparently it's impossible to get one, tried asking on Reddit and nobody seems to know exactly why, nor we ever had any warnings about it. Could we maybe have transparency and know in which cases some stats are unobtainable? Some supposed you can only get -IPS for the main Damage of the weapon but no, there are plenty of -slash -puncture Plague Kripath rivens.
And, maybe most importantly, why?

List of sold Rivens
Velocitus SOLD for 774pl + R0 Arcane Guardian
Kronen SOLD for 1000pl
Cyanex SOLD for 900pl
Akstiletto SOLD for 950pl + Shotgun Veiled Riven
Ignis SOLD for 935pl + Ammo Drum
Hikou SOLD for 150pl
Detron SOLD for 780pl Paracesis SOLD for 1900pl Imperator+Larkspur SOLD for 2000pl
Catchmoon SOLD for 1600pl
Baza+Atomos SOLD for 1450pl
Daikyu SOLD for 800pl
Vectis SOLD for 1350pl
Tatsu SOLD for 700pl
Gram SOLD for 1050pl
Opticor SOLD for 1050pl
Lanks SOLD for 800pl
Arca Plasmor SOLD for 550pl
Jaw Sword SOLD for 800pl
Skana SOLD for 138pl
Wolf Sledge SOLD for 650pl

Before starting I'd like to make a quick disclaimer which I feel is rather necessary. All the time I jump into a post that brings up the terrible state in which Taveuni - Kuva Survival is I notice way too many comments disregarding what X or Y guy has to say just because in their eyes Rivens and Kuva are content in which one shouldn't spend or invest time in. To me, Rivens are what currently keeps me engaged into Warframe and it's a wonderful addition I thank DE for. They satisfy the needs of collectors like me who want to own something unique and hard to aquire and also the needs of traders - now that every prime part goes down to 1 pl two days after launch thanks to market sites *cough cough*.
If it's not your content, don't bother others who genuinely want to fix it for the health of the game, thanks. I don't snipe every conclave post just because I don't play it. Kuva Floods and Siphons: I think we can all agree that these are in a pretty good state. In fact many believe them to be the best way to farm kuva. The only complaint I have here are mostly Kuva Floods/Siphons Survivals. Many times the Kuva Siphon is hidden in some hidden part of the map and it's impossible to find. Now why do I propose this as a problem: in sabotages missions, for example, there is actually skill involved - would it be remembering the spots, quickly looking into a room, following the sound of the hidden cache - while in finding a random siphon that spawns who knows where this time there isn't. My solution to this would be rather simple - and will be linked to ideas on Taveuni as well - as I 100% believe the laziest answer is the best answer: a Samodeus Scanner. How hard could it be to take the current Symaris Scanner and tune it a bit just to find Siphons rather than Synthesis Targets? I also love the idea because it gives long term potential for the Cephalon Samodeus character itself. Do we really wanna keep him as the hated guy who just messages you to inform you that your OP Supra or Rubico riven is now worthless? Taveuni Kuva Survival: Now I'll come to the actual title of this post: Endgame Content.
Now, let's sit back for a moment and think about what endgame for Warframe is. Because I personally experienced it and it has been - kinda - taken away. You know what endgame content has been for me? Ash Prime Systems.
Now we can all 100% agree that the Relic system has made prime farming 100% less tedius. God I even thought it was a stupid move on their part since I farm most Prime Access' in a few days after release. BUT, if I'll ever walk away from Warframe what I will remember, for sure, is gonna be this: T3 Survival in the Void.
I'm gonna quickly go over the details that this mission had to offer:
While Fissure Survivals give you a chance to instert a relic every 5 minutes (just like every other endless), in T3 Survivals and other T# missions one single "Void Key" could have been spent for the entirity of the mission.
Due to that you had a strong incentive to remain in mission as long as possible. Why would you ever do that now with fissures?
Incentive to play in group. We are all familiar with Relic Shares right? Imagine one that doesn't end after 2 minutes.
Therefore my ideas for Kuva Survival Taveuni want to bring these aspects back into Warframe.
1. Increase the amount of Kuva earned per harvester. Making something easier and less tedius to aquire won't stop people from doing it, but rather the opposite. I let them DE-cide the amount: I even stated in a previous post that a simple 50 kuva buff would be insanely appreciated and make things a lot less sufferable.
2. An incentive to remain in mission and face harder content. My idea would be to spawn a Kuva Siphon of some sort at Rotation C, 20 minutes that has to be tracked down with the Samodeus Scanner. This could either be a normal Siphon OR, a lot better, a Siphon that in addition to the normal rewards increases the amount of Kuva harvested per harvester.
3. An incentive to play with other people and organized groups. A system like this gives you new ways to maximize your rewards and toy around with the rewards, suddendly skill can be taken into account. Wouldn't it be interesting to see squads elaborating strategies like keeping 7 harvesters free until you reach the 20 minutes Kuva boost and then opening all of them and so on for different waves? At least it makes you feel more engaged than going solo with Khora and pressing 4 every 50 seconds, to say the least. And yes we all do it like this don't hide it.
Another possible idea on the 20 minutes Siphon in Taveuni. One of the best feelings that never gets old is the mistery surrounding Derelict Vaults. Honestly there's no other content like Derelict Vaults that keeps the same amount of hype and discovery that felt the same right when I started Warframe and now that I have basically all that I need achieved. This new Siphon could be something just like the Orokin Vault that demands you to consume a Riven in order to boost your rewards. Perhaps maybe the higher the amount of rolls on it could amount to more Kuva boosted into the regular harvester.
Now again, what would you rather play, a mission where you spend one hour pressing "4" every 50 seconds to give you 4 chances in an RNG roulette, or this?

I'm happy that you're the onlyone who didn't read all my message and stopped at the first sentence.
All I can say is take a deep breath, read it fully and then make up your mind then. I use Khora all the time - as stated in my comment 😉 - which wasn't a support to his demand to nerf the ability, if you would have read what I said.
So yes, saying that you can afk using her 4 is a FACT and that's why people go Kuva Surv solo nowadays. Anyways I also mentioned how this is a necessary evil that should be kept in the game.

I'm pretty sure if he used the word "rework" instead of "nerf" he wouldn't have received all these angry comments towards him.
You have to see where he is coming from: with a proper build, you can jump solo into a Kuva survival and stay there for more than 30 minutes and your Strangledome will do all the work while you watch a movie in the background. Frost cannot put a globe and go afk, nor any other defensive frame. Can we agree on this?
HOWEVER (is this however big enough to avoid any kind of blind rage and push you to read further? 😮) at this point I think Khora and the way she is designed is a necessary evil. I took Kuva Survival as an example: we go through repetitive and dull content sometimes and having a way to cheese it it's not bad for the game in my opinion.
Therefore, I know it's like "morally" wrong to have an ability that does what a nekros, frost and - idk - dps-bastille with mostly no effort but a button press, but hey, I personally really don't want to see it changed.

Also are there any plans to change the Kuva Survival? Right now it is mandatory to have a resource booster and after one hour you end up with only 4 rolls on your riven which we all know it's RNG based and feels frustrating. Could it be transformed into a disruption or buff the rewards even by a little?